linear reset curve (Munchkin), nonlinear radiation

Jay_12

Hello Jim,

tekmar has long recognized heating units are non-linear and that is why our controls have characterized heating curves. Attached is the essay E003 that discusses reset ratios and characterized heating curves.

Jay www.tekmarcontrols.com 1-250-545-7749

Plumbob

how to fix?

I set my Munchkin reset curve to go from 95F@65F to 180F@0F (see picture below). The high point is based on my experience of last year, where my old CI boiler ran for about 15 hours with 180F water on a 0F (avg) day.

Well, on a 50F day the Munchkin runs only about 8 hours, in other words the water is too hot. But on a 35F day it runs 24 hours and fails to fully heat the house, i.e. the water is too cold. We hven't had a 0F day yet, but no doubt it will run 15 hrs with 180F water, just like my old boiler did, i.e. the water will again be too hot.

So obviously the baseboard response has a pronounced "hump" at medium temperatures. I believe this is a known characteristic. So now I am forced to set water temperatures much higher than necessary, just to get over the hump.

Why are reset "curves" linear? Isn't it pretty easy these days, with a 50 cent microprocessor, to do 10-point curves rather than 2-point lines?

What can I do to follow the baseboard's nonlinear characteristics more closely, so that I am not using too-hot water in very cold weather or too-cold water in medium weather?

Plumbob

Yes, that's just what I need.

But if I tried to attach a Tekmar to a Munchkin, I'd lose the Munchkin's ability to modulate (it modulates based on how far away it is from its internal target tmperature, which would have to be set at 180 if a Tekmar is controlling the water temperature via on/off). So it's six of one, half dozen of the other.

I've heard of the 263 modulating controller, but it is not on the tekmar web page. And I don't know if it can be directly attached to the Munchkin. or if I need to buy things that Munchkin won't sell me unless I take a course from them (!)

hydronicsmike

Straight Reset Curves is kind of like Football (maybe??)

Why do you call Football - Football? Since the ball (egg)only gets kicked when the it is punted. For the majority of the game the ball is either thrown or carried. So actual Football had to be called Soccer.

You ever seen a straight curve?

Anyways, Jay's got it covered. I am just here to entertain now.

hydronicsmike

HTP...

...should soon have an interface module available that allows a tekmar Control to modulate a Munschkin boiler. At least thats the last I heard, right Chuck??

Plumbob

Paul Rohrs_2

Right Mike!!

I have three on order right now. (Peerless) Model 91488 interface module.

It will take the 0-10V DC signal from the Munchkin Pinnacle boilers and adapt it to the 4-20ma necessary
for the Tekmar 263 to control it. Look at #5 from this excerpt from the Peerless Pinnacle IOM.

Regards,

PR